\documentclass[border=10pt]{standalone}
\usepackage{pgfplots,tikz,amsmath}
\usepackage{filecontents}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{colorbrewer}
\usepgfplotslibrary{colorbrewer}
%\usepgfplotslibrary{colormaps}
%\usepackage{pgfplotstable}
\usepgfplotslibrary{external}
% \tikzexternalize[shell escape=-shell-escape]
\begin{document}

\begin{tikzpicture}
\begin{axis}[xlabel=$x$,
ylabel= $c(x)$,
width = 5.0 cm,
height = 3.0 cm,
transpose legend,
legend columns=-1,
%grid = both,
ylabel near ticks,
xlabel near ticks,
xmin=0.0,
xmax = 1.0,
%cycle list/RdGy-11,
%cycle list/Paired-10,
cycle list name=Paired-10,
%cycle list name=linestyles*,
]
\addplot+[mark = none, smooth, thick] table[x index=0,y index=1] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=25] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=49] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=73] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=97] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=121] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=145] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=169] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=193] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=217] {tunneling.txt};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
\begin{axis}[xlabel=$x$,
ylabel= $\varrho_a(x)$,
width = 5.0 cm,
height = 3.0 cm,
transpose legend,
legend columns=-1,
%grid = both,
ylabel near ticks,
xlabel near ticks,
xmin=0.0,
xmax = 1.0,
%cycle list/RdGy-11,
%cycle list/Paired-10,
cycle list name=Paired-10,
%cycle list name=linestyles*,
]
\addplot+[mark = none, smooth, thick] table[x index=0,y index=2] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=26] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=50] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=74] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=98] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=122] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=146] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=170] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=194] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=218] {tunneling.txt};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
\begin{axis}[xlabel=$x$,
ylabel= $\varrho_s(x)$,
width = 5.0 cm,
height = 3.0 cm,
transpose legend,
legend columns=-1,
%grid = both,
ylabel near ticks,
xlabel near ticks,
xmin=0.0,
xmax = 1.0,
%cycle list/RdGy-11,
%cycle list/Paired-10,
cycle list name=Paired-10,
%cycle list name=linestyles*,
]
\addplot+[mark = none, smooth, thick] table[x index=0,y index=3] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=27] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=51] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=75] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=99] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=123] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=147] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=171] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=195] {tunneling.txt};
\addplot+[mark = none, smooth, thick] table[x index=0,y index=219] {tunneling.txt};
\end{axis}
\end{tikzpicture}
%
%\begin{tikzpicture}
%\begin{axis}[xlabel=$t$,
%ylabel= $x_{\text{loc}}$,
%width = 4.0 cm,
%height = 4.0 cm,
%transpose legend,
%legend columns=-1,
%%grid = both,
%ylabel near ticks,
%xlabel near ticks,
%xmin=0.0,
%xmax = 1.0,
%%cycle list/RdGy-11,
%%cycle list/Paired-10,
%%cycle list name=Paired-5,
%%cycle list name=linestyles*,
%]
%\addplot+[each nth point={3}, mark = none, smooth, very thick, black] table[x index=0,y index=1] {xLoc.txt};
%\end{axis}
%\end{tikzpicture}

\end{document}